The dual effect of lithium ions on sodium efflux in skeletal muscle.
Sartorius muscle cells from the frog were stored in a K-free Ringer solution at 3 degrees C until their average sodium contents rose to around 23 mM/kg fiber (about 40 mM/liter fiber water). Such muscles, when placed in Ringer's solution containing 60 mM LiCl and 50 mM NaCl at 20 degrees C, extruded 9.8 mM/kg of sodium and gained an equivalent quantity of lithium in a 2 hr period. The presence of 10(-5)M strophanthidin in the 60 mM LiCl/50 mM NaCl Ringer solution prevented the net extrusion of sodium from the muscles. Lithium ions were found to enter muscles with a lowered internal sodium concentration at a rate about half that for entry into sodium-enriched muscles. When sodium-enriched muscles labeled with radioactive sodium ions were transferred from Ringer's solution to a sodium-free lithium-substituted Ringer solution, an increase in the rate of tracer sodium output was observed. When the lithium-substituted Ringer solution contained 10(-5)M strophanthidin, a large decrease in the rate of tracer sodium output was observed upon transferring labeled sodium-enriched muscles from Ringer's solution to the sodium-free medium. It is concluded that lithium ions have a direct stimulating action on the sodium pump in skeletal muscle cells and that a significantly large external sodium-dependent component of sodium efflux is present in muscles with an elevated sodium content. In the sodium-rich muscles, about 23% of the total sodium efflux was due to strophanthidin-insensitive Na-for-Na interchange, about 67% being due to strophanthidin-sensitive sodium pumping.
D000818:Animals; D001001:Anura; D001693:Biological Transport, Active / Q000187:drug effects*; D002297:Cardanolides / Q000494:pharmacology; D007477:Ions / Q000494:pharmacology; D008094:Lithium / Q000494:pharmacology*; D009132:Muscles / Q000378:metabolism*; D010783:Photometry; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D012975:Sodium Isotopes; D013395:Sucrose / Q000494:pharmacology
D002297:Cardanolides; D007477:Ions; D012975:Sodium Isotopes; D013395:Sucrose; D008094:Lithium; D012964:Sodium; D011188:Potassium